Alloy composition and method of forming the same



United States Patent 3,464,817 ALLOY COMPOSITION AND METHOD OF FORM- ING THE SAME Emil S. Griffiths, Albany, N.Y., assignor to CMP Industries, Inc., Albany, N.Y., a corporation of New York No Drawing. Filed Mar. 17, 1966, Ser. No. 535,027 Int. Cl. C22c 19/.00 US. Cl. 75-171 15 Claims ABSTRACT OF THE DISCLOSURE An alloy suitable for use in forming dentures and other dental prostheses contains, in weight percent, about 10% to 28% chromium, about 5% to 12% molybdenum, about 3% to 7% manganese, about 0.2% to 2% beryllium, about 2% to 6% aluminum, up to about 22% cobalt and the balance essentially nickel. This alloy is characterized by high strength, toughness, good ductility, good fluidity in the molten state, and controlled shrinkage when cast. These properties cause the alloy to abrade readily for ease of polishing, permit deformation by bending without fracture when necessary to mechanically adjust parts formed of the alloy in dental prostheses, and allow the casting of thin or attenuated sections and other pieces within close tolerances. The alloy preferably is formed by melting the alloying elements in a preferred sequence and maintain ing selected alloying elements beneath the surface of the molten pool to prevent oxidation.

My invention relates to alloy compositions and the method of forming the same and particularly to alloy compositions suitable for the production of dental prostheses. Also the invention relates to the method for the production of such alloy compositions.

Dental alloy compositions adapted for prosthetic articles are discussed in United States Patent No. 2,631,095, granted Mar. 10, 1953, for Alloy Adapted for Prosthetic Articles. The alloy system discussed in US. Patent No. 2,631,095 employs chromium, molybdenum, beryllium, manganese and copper with the balance of the alloy being a combination of cobalt and nickel. However, in the past, as in the alloy described in US. Patent No. 2,631,095, ease of polishing, although a desirable property, had to be sacrificed in order to provide an alloy with sufiicient yield strength.

Because the prosthetic articles or appliances cast from the alloy are used in the mouth, the space available for their insertion is always limited and for this reason the alloy must be exceptionally strong. When casting partial denture prostheses, high yield strength is essential if the alloy is to function properly since the clasps used to retain the appliance are small in cross section and the retention provided for mounting the artificial teeth is also thin and attenuated. Ordinarily, as yield strength values are increased, hardness also increases but ease of polishing decreases.

Yield strength and ease of polishing are not the only important characteristics. Ductility is important since the clasps must permit adjustment without the risk of shearing or breaking. In order to achieve an accurate fit when the appliance is inserted in the mouth, the net casting shrinkage must be controlled within rather limited tolerances. Further, because the appliances are constructed with rather thin attenuated areas of relatively small cross section, the alloy must be highly fluid at casting temperature so that it will flow readily into these restricted openings and not form voids or cavities therein which would render the appliance unusable. This is true especially with 3,464,817 Patented Sept. 2, 1969 full denture prostheses or veneer castings for full bridge work.

It is an object of my invention to overcome the difficulties heretofore encountered and it is a primary object of my invention to provide an alloy composition suitable for use as a dental prosthesis which is readily abraded and polished but which will maintain hardness, yield strength, and sufficient ductility, without the risk of shearing or breaking the appliance when it is adjusted for insertion in the mouth.

It is also an object of my invention to provide an alloy which will maintain a high luster after it is completed and which will resist discoloration after prolonged use.

My invention generally contemplates providing an alloy composition suitable for the production of dental prostheses in which a plurality of elements in desired proportions comprise chromium, molybdenum, manganese, beryllium, aluminum, cobalt and nickel. The alloy is characterized in that it is easily cast into an appliance which has increased yield strength and improved ductility, but still possesses the ability to abrade readily for ease of polishing. Further, the novel combination of the elements comprising the alloy produces an alloy in which substantially all of the elements are combined with a minimum loss of the alloy due to oxide formation.

I have found in my new alloy composition that unexpected results are obtained by alteration of the alloy systern disclosed in US. Patent No. 2,631,095, referred to above, so as to achieve the desired characteristics disclosed therein and with the added improvement in the ability of the new alloy to abrade readily so as to permit ease of polishing of the prosthetic articles without the risk of shearing or breaking the appliance when it is adjusted for insertion in the mouth, By changing the alloy system and utilizing aluminum in place of copper, and reducing the cobalt content with disregard of the cobalt-nickel ratio as taught in US. Patent No. 2,631,095, unexpected results are achieved. Thus by employing an aluminum content not in excess of 6% and a cobalt content not in excess of 22% and without the necessity of maintaining a nickelcobalt ratio, an improved alloy system useful for full and partial prosthetic articles is achieved. As stated previously, my new alloy is readily abraded and polished without any loss of the necessary physical characteristics that must be present for prosthetic articles of this type.

The elements comprising my new alloy composition are set forth below and their percentages, by weight, of the total composition are:

The preferred ranges of elements forming my improved alloy composition are set forth below and their percentages, by weight, of the total composition are:

Percent Chromium 12-24 Molybdenum 5-7 Manganese 3-5 Beryllium 0.5-1 Aluminum 2-4 Cobalt 0-3 and 12-15 or 3-6 and 18-22 Nickel Balance It is to be noted that the cobalt in the preferred composition lies within the ranges of from approximately 0 to 3% and 12 to 15%. It has been found that such an alloy composition having the percentage of cobalt set forth therein exhibits excellent qualities and physical characteristics for partial dentures while the ranges of cobalt of approximately 3 to 6% and 18 to 22% exhibit excellent qualities and physical characteristics for full dentures.

An alloy suitable for use as a partial denture is characterized by its ability to adjust without shearing; that is, the attenuations which are the clasping or clamping means for holding the denture in the mouth must be sufiiciently ductile and resilient so that when the dental appliance is adjusted for use these attenuations will not shear. When a full denture is employed it is not necessary for it to exhibit the degree of ductility and resiliency that is required in a partial denture. However, the alloy employed, whether used as a partial or full dental appliance, must have a characteristic of being capable of exhibiting sufficient casting fluidity, i.e., the ability to form thin, resilient and ductile films when employed as a full denture and the ability to flow readily into cavities forming the attenuations or clasping means in a partial denture. All of these chearacteristics are exhibited by my new alloy.

In making my alloy composition it is preferred that the elements be combined by employing induction or high frequency heating, although other accepted heating procedures may be employed.

I have found that in forming my alloy certain of the elements when added to the melt in a preferred sequence, produce an alloy having the desired physical characteristics which include high yield strength, increased ductility, suflicient hardness, and the ability to abrade readily for ease of polishing. When charging a crucible with my improved composition, the nickel is added first and a partially molten pool is formed. When the nickel is sufliciently liquid to permit forcing additional material below the surface of the molten pool, molybdenum is added and immediately forced beneath the surface so that it will not be exposed to the air and be lost by oxide formation. It should be noted that the molybdenum does not melt but rather dissolves in the liquid pool. However, it would volatilize as an oxide if heated in air. Thus, it is essential that the molybdenum be completely immersed if good recovery of the molybdenum is to be obtained.

The temperature of the molten pool of nickel will generally be 2650 F. before the addition of molybdenum as described above. However, where prealloyed materials are used as part of the alloy mix the temperature of the melt prior to the addition of molybdenum can be as low as 2400 F.

The chromium is added next. This, too, is forced under the surface of the liquid pool as much as possible. Since the bulk of the chromium added is much greater than that of the molybdenum, it may cause the nickel which has already liquified to freeze. No further additions are made until the pool again starts to liquify.

When this occurs the aluminum is added. The aluminum is low melting. However, it has been found that when it is added to a melt having a relatively high nickel content, a high melting nickel aluminum compound is formed and unless sufficient time is allowed for the high melting components to dissolve and disperse throughout the melt, serious segregation of the high melting compound may occur. The reaction causing the formation of the high melting compound is apparently exothermic and the liberation of this heat helps to further liquefy the pool and stimulate the solution of both the chromium and the aluminum.

In alloys which are to contain cobalt, the cobalt is added at this time.

After the melt has been heated for a sufiicient time to completely dissolve all of the components and form a homogeneous pool, the sides of the crucible are scraped down to remove any dross which floats to the surface and can be skimmed off. At this time the melt is at a temperature of approximately 2700= F. and is deoxidized with an addition of calcium-silicon-manganese. The reaction products for this deoxidation are skimmed from the surface in order to leave the surface clean.

The manganese is then added. This dissolves very quickly. Any slight dross which forms is skimmed from the surface so that the pool again is clean.

The beryllium addition is then made. Because of the low specific gravity of the beryllium it will tend to float on the surface and the operator must use a skimming rod to force it beneath the surface of the molten pool.

The temperature of the melt is checked and heating continued until a temperature of 2800 F. is reached. At this point the sides of the crucible are again scraped to remove any dross and the surface of the pool skimmed to remove the material which floats to the surface. The alloy can then be poured.

The following examples illustrate alloy compositions and their percentages, by weight, of the total composition when made in accordance with the method set forth above:

EXAMPLE 1 Percent Chromium 15 Molybdenum 5 Manganese 3.5 Beryllium 0.8 Aluminum 3.0 Cobalt 0 Nickel Balance EXAMPLE 2 Percent Chromium 15 Molybdenum 10 Manganese 3.5 Beryllium 0.8 Aluminum 3.0 Cobalt 0 Nickel Balance EXAMPLE 3 Percent Chromium 15.0 Molybdenum 5.0 Manganese 3.5 Beryllium 0.8 Aluminum 3.0 Cobalt 10.0 Nickel Balance As previously indicated, and set forth in Examples 1-3, alloy compositions made in accordance with the method described above are suitable for use as partial dentures and exhibit the improved physical characteristics as set forth hereinabove.

EXAMPLE 4 Percent Chromium 10.0 Molybdenum 5.0 Manganese 3.5 Beryllium 0.8 Aluminum 3.0 Cobalt 0 Nickel Balance EXAMPLE 5 Percent Chromium 15.0 Molybdenum 0 Manganese 3.5 Beryllium 0.8 Aluminum 3.0 Cobalt 0 Nickel Balance 5 6 EXAMPLE 6 be helpful in understanding my invention. Tables I and II Percent show variations in physical characteristics achieved by Chromium 15 o varying the content of the ingredients of the alloy compo- Molybdenum sition when'made in accordance with the method de- Ma anese 5 scribed herein. The variations are illustrated relative to the B physical characteristics of Rockwell hardness, resilience, 'Y 111111 ductility (toughness), liquidus (lowest temperature in de- A u ml grees F. at which the alloy composition is completely Cobalt 0 liquid), and the preferred use of the particular alloy com- Nickel al position wtih regard to its usefulness as a partial or full denture, or both. Also in Table II the alloys have been EXAMPLE 7 grouped on the basis of the ingredient being varied so that percent the eifect of the variation on Rockwell hardness, resilience, Chromium 150 toughness, and in some instances the liquidus temperature Molybdenum is readily apparent. As 1s apparent from the table, these Manganese 35 properties do not vary linearly with changes in the amount Beryllium (L8 of the ingredients employed. Aluminum 3 0 TABLE I.COMPOSITION Cobalt 0 Alloy No. Ni Co Cr Mo Mn Be Al Ni k l Balance 65.7 0 22.0 5.0 3.5 0.2 3.0 3.3 8 5.0 3.5 0.8 2.0 As previously indicated and as set forth in the alloy com- 731 5 0 1510 &3 '3 31?) positions of Examples 4-7, alloy compositions made in 3;? 3 2'3 2'3 5'2 3'8 accordance with the method described above are suitable Egg 8 ig-g 28 7 3 8:8 3:0 for use as full dentures and exhibit the improved physical 71: a 0 15:0 510 315 21?) 3:3 characteristics as set forth hereinabove. o

TABLE II Component Rockwell Alloy N0. varied, percent hardness Resilience Toughness K1 31 1533: Use

Chromium EX. 1..-... 15 C32 Excellent Excellent P -t' 1. E5122": 02 2 Soft do 2, 730 Fii lli 60 .I. 22 27 76 27.7 29 F Molybdenum Ex.5 0 024 Ex. 10 33 79 15 44 82 B90 Dead Exc 11 t tigi C Very Good Goo iL 2,460 Part i al. 34 do...-... Falr-good Do.

Ex.6 0 B89 Ver (1 d E 103 6.0 041 exciuffianwu. Nifiiiffi "2E9- bo Manganese 95 0 C30 Fair-soft Ex 11 t 2,57 D 96 7- 28 Good Faififi 2, 482 Partial.

Cobalt 5. g Fair-soft Excellent 2, 550 Full and partial:

20 "do 2, 535 Partial.

ea do Full.

EXAMPLE 8 I claim:

Percent 1. A method of forming an alloy suitable for casting Chromium dental prostheses having high strength and the ability to Molybdenum 3-5 abrade readily for ease of polishing and sufficient ductile Manganese characteristcs for readily adjusting said prostheses comitirylll m prising melting said alloy by heating, sequentially control- C g ll z' ling the addition of the elements forming said alloy which Nigel consists essentially of about 10% to 28% chromium,

-- about 5% to 12% molybdenum, about 3% to 7% man- The composition of Example 8 is an example of an alloy which is suitable for use both as a partial or full denture and exhibits the improved characteristics of my new alloy composition.

The alloy compositions set forth in Table I below and when made in accordance with the method described herein and when cast into a dental appliance exhibit the improved and unexpected physical characteristics concerning my new alloy composition when the dental appliance is used for its preferred use.

A consideration of the alloy compositions set forth in the foregoing examples and in Tables I and II below will ganese, about 0.2% to 2% beryllium, about 2% to 6% aluminum, up to about 22% cobalt and the balance essentially nickel, said addition being accomplished by charging nickel into a crucible; heating the crucible to melt the nickel and form a molten pool thereof; adding the molybdenum so that it is submerged in the molten nickel pool; sequentially adding chromium, aluminum, cobalt and manganese to the nickel and molybdenum molten pool and then adding the beryllium so that it is maintained beneath the surface of the formed molten pool so as to prevent oxide formation and loss of beryllium in the final alloy mixture whereby a substantially homogeneous mixture of molten elements are formed.

2. The method of forming an alloy as set forth in claim 1 wherein said alloy mixture is melted by induction heating and then cast into a desired dental prosthesis.

3. An alloy suitable for use in forming dental prostheses and the like and consisting essentially, in weight percent, of about 10% to 28% chromium, about 5% to 12% molybdenum, about 3% to 7% manganese, about 0.2% to 2% beryllium, about 2% to 6% aluminum, up to about 22% cobalt and the balance essentially nickel; said alloy being characterized by high strength and good toughness and ductility, good fluidity in the molten state, and controlled shrinkage when cast, whereby the alloy will abrade readily for ease of polishing, can be substantially deformed by bending without fracture when necessary to mechanically adjust parts formed of the alloy in dentures or other phostheses, and is capable of forming thin or attenuated sections within close tolerances when cast.

4. An alloy suitable in forming partial dentures in accordance with claim 3 which consists essentially of about 15% chromium, about 10% molybdenum, about 3.5% manganese, about 0.8% beryllium, about 3.0% aluminum, and the balance essentially nickel.

5. An alloy suitable in forming partial dentures in accordance with claim 3 which contains up to about 3% cobalt.

6. An alloy suitable in forming partial dentures in accordance with claim 3 which contains about 12% to 15 cobalt. I

7. An alloy suitable informing full dentures in accordance with claim 3 which contains about 3% to 6% cobalt.

8. An alloy suitable in forming full dentures in accordance with claim 3 which contains about 18% to 22% cobalt.

9. An alloy particularly suitable for use in making dental prostheses and the like and cosisting essentially, in weight percent, of about 12% to 24 %chromium, about 5% to 7% molybdenum, about 3% to 5% manganese, about 0.5% to 1% beryllium, about 2% and 4% aluminum, up to about 22% cobalt and the balance essentially nickel; said alloy being characterized by high strength and good toughness and ductility, good fluidity in the molten state and controlled shrinkage when cast, whereby the alloy will abrade readily for ease of polishing 8 can be substantially deformed by bending without fracture when necessary to mechanically adjust parts formed of the alloy in dentures or other dental prostheses, and is capable of forming thin or attenuated sections within close tolerances when cast.

10. An alloy suitable in forming partial dentures in accordance with claim 9 which consists essentially of about 15% chromium, about 5% molybdenum, about 3.5% manganese, about 0.8% beryllium, about 3.0% aluminum, and the balance essentially nickel.

11. An alloy suitable in forming partial dentures in accordance with claim 9 which consists essentially of about 15% chromium, about 5% molybdenum, about 3.5% manganese, about 0.8% beryllium, about 3.0% aluminum, about 10% cobalt, and the balance essentially nickel.

12. An alloy suitable in forming full dentures in accordance with claim 9 which consists essentially of about 15% chromium, about 5% molybdenum, about 3.5% manganese, about 0.8% berryllium, about 3.0% aluminum, about 20.0% cobalt, and the balance essentially nickel.

13. An alloy suitable in forming full dentures in accordance with claim 9 which consists essentially of about 15% chromium, about 5% molybdenum, about 3.5% manganese, about 0.8% berryllium, about 3.0% aluminum, about 5% cobalt and the balance essentially nickel.

14. An alloy suitable in forming partial dentures in accordance and claim 9 which contains up to about 3% cobalt.

15. An alloy suitable in forming partial dentures in accordance with claim 9 which contains about 12% to 15 cobalt.

References Cited UNITED STATES PATENTS 1,942,150 1/1934 Rohn -171 2,072,911 3/ 1937 Touceda 75-171 2,089,587 8/1937 Touceda 75-171 2,206,502 7/ 1940 Heiligman 75-171 2,469,718 5/ 1949 Edlund et al. 75-171 RICHARD O. DEAN, Primary Examiner US. Cl. X.R. 32-2 

